Recent spam increase & greylisting

[grunty]

Hi everyone

We have seen a marked increase in the volume of spam that we're receiving in April. I was wondering if everyone else is seeing a similar trend.

Here is the graph from Zimbra showing the volume increase...



We use an outsourced greylisting service. They suggest that these trends are just due to wiser spammers, however I'm not so sure. I wonder whether greylisting is broken on one of there mx servers.

I assume that there are some of you out there using Zimbra with greylisting - have you seem the same as me?

Does anyone know an easy way for me to test greylisting? - so I can reassure myself that it's working OK.

Thanks

Al